1. Field of the Invention
The present invention relates to methods for increasing hydrolysis of cellulosic material with an enzyme composition.
2. Description of the Related Art
Cellulose is a polymer of the simple sugar glucose linked by beta-1,4-bonds. Many microorganisms produce enzymes that hydrolyze beta-linked glucans. These enzymes include endoglucanases, cellobiohydrolases, and beta-glucosidases. Endoglucanases digest the cellulose polymer at random locations, opening it to attack by cellobiohydrolases. Cellobiohydrolases sequentially release molecules of cellobiose from the ends of the cellulose polymer. Cellobiose is a water-soluble beta-1,4-linked dimer of glucose. Beta-glucosidases hydrolyze cellobiose to glucose.
It is well known in the art that oxidation of biomolecules such as DNA, lipids, or protein is a significant issue in biological systems. Consequently, treatment with a peroxidase may improve the performance of cellulose-hydrolyzing enzyme systems.
Different peroxide-decomposing enzymes often have different specificities and potencies. For example, catalase is very efficient only at high levels of hydrogen peroxide (0.1 M or above) because of its high Michaelis constant, Km, on this substance (Km ranges from 0.1 to 1 M: see Nicholls et al., 2001, Advances in Inorg. Chem. 51: 52-106; and Masaki et al., 1998, Archives of Dermatological Research 290: 113-118). At low peroxide levels, a peroxidase can be significantly more efficient (than catalase) to decompose the peroxide, because of the enzyme's high affinity (sub-mM ranges) for the peroxide. For example, horseradish peroxidase, an archetypical peroxidase, has a Km of 0.02 mM on hydrogen peroxide or ethyl hydroperoxide (Kedderis and Hollenberg, 1983, J. Biol. Chem. 258: 8129-8138), and glutathione peroxidase has a Km of 0.025-0.06 mM (Masaki et al., 1998, supra). Since many biomass conversion techniques are prone to generate low level peroxide, peroxidase may be more effective than catalase to remove the peroxide to improve cellulose hydrolysis.
The present invention provides methods for increasing hydrolysis of cellulosic materials with enzyme compositions.